Bast fibers for plastics reinforcement and preparation method thereof

ABSTRACT

The present invention refers to bast fibers for plastics reinforcement and preparation method thereof. The bast fibers are composed of the following components by weight ratio; 100 pts.wt. chopped bast fibers, 0.1˜100 pts.wt. bast fiber treating agent, 1˜10 pts.wt. Functional Polyolefin wax, 0.1˜10 pts.wt. coupling agent and 0.1˜0.5 pts.wt. antioxidant. The method includes the steps of: firstly, cut chopped bast fibers and soak them in sodium hydroxide solution, agitate the mixture, after rinse and drying of water, soak the fibers in the aqueous solution of bast fiber treating agent, then dry them and obtain surface-treated chopped bast fibers; secondly, add in order the chopped fibers, the coupling agent, the Functional Polyolefin wax and the antioxidant to a preheated kneader, agitate the mixture and thus obtain bast fibers for plastics reinforcement. Chopped bast fibers according to the invention present good color, rigidity and heat resistance, as well as excellent compatibility with plastics, and can be used in the preparation of high-performance short-bast-fiber\plastic composites, as reinforcement in the plastic matrix.

FIELD OF THE INVENTION

The invention refers to the natural fiber composite materials and wood-plastic composite materials, especially refers to bast fibers for plastics reinforcement and preparation method thereof

BACKGROUND OF THE INVENTION

In recent years, research in natural plant fiber composite materials and wood-plastic composite materials has been in the ascendant. This is on the one hand because of the wide range of sources of natural plant fibers and relatively lower prices, and on the other hand due to the trend of natural plant fiber reinforced plastics being used as a replacement of mineral fiber reinforced plastics.

Most natural plant fibers are, in long fibrous form or after being formed into a fiber mat, compiled into hot press molding with thermosetting resin, while can not be added directly into thermoplastic plastics for injection molding as glass fibers; in addition, on the one hand, natural plant fibers show strong polar and hydrophilic qualities due to the high density of hydroxyl groups on fiber surface, which induces plant fibers to be poorly compatible with non-polar or weakly polar plastics and further leads to rather poor performance of composite materials thus made; on the other hand, plant fiber reinforced plastics are difficult for processing, in particular for injection molding, in light of the large volume and high filler content of plant fibers, as well as strong frictions existing between fibers and plastics, fibers and equipment, and among fibers. To improve the interface compatibility between plant fibers and plastics, the main solution at present is to add interfacial compatibilizer, one type is coupling agent, such as silane coupling agent, titanium coupling agent, aluminate coupling coupling agent, RE agent, isocyanate coupling agent, etc., and the other type is the graft or copolymer of maleic anhydride with polyolefin. For one thing, most of the coupling agents are in liquid form with less dosage, difficult for even dispersion in plant fibers and thus weaking the coupling effect, so special processing equipment is required for industrial applications; for another, most grafts or copolymers of maleic anhydride with polyolefin are in granular form, easy for dispersion in plastics and plant fibers, but the low grafting ratio brings negative effects on the improvement of the interface bond strength. Even so, composites filled with a large number of plant fibers and plastics further presents the difficulty in extrusion or injection molding. Various processing aids, such as olefin wax, amide wax, stearic acid, zinc stearate, calcium stearate, etc., have been developed to solve the problems in processing composite materials of plant fibers and plastics, but adding too much processing aids will also lower the performance of the composite materials.

SUMMARY OF THE INVENTION

To overcome the shortcomings of the existing technology, the primary objective of the present invention is to provide bast fibers for plastics reinforcement.

A second objective of the present invention is to provide a method for producing said bast fibers for plastics reinforcement.

To achieve these objectives, the present invention provides technical solutions as follows: bast fibers for plastics reinforcement, characterized in that: the bast fibers for plastics reinforcement consist of the following components by weight ratio:

Chopped bast fibers 100 pts.wt. Bast fiber treating agent 0.1~100 pts.wt. (preferred 10~80 pts.wt.) Functional Polyolefin wax 1~10 pts.wt. Coupling agent 0.1~10 pts.wt. Antioxidant 0.1~0.5 pts.wt.

The chopped bast fibers are chosen from at least one of the following fibers: ramie fiber, flax fiber, agave fiber, jute fiber and agotai fiber.

The bast fiber treating agent is urea-formaldehyde resin prepolymer, trimethylol melamine resin or hexamethylol melamine resin.

The Functional Polyolefin wax is chosen from at least one of the following components: metallocene polyethylene wax, metallocene polypropylene wax, metallocene polyolefin wax, oxidized metallocene polyolefin wax and maleic-anhydride-grafted metallocene polyolefin wax.

The coupling agent is chosen from at least one of the following components: silane coupling agent, titanium coupling agent, aluminum coupling agent, isocyanate coupling agent and rare-earth coupling agent.

The antioxidant is composed of antioxidant 1010 and antioxidant 168, with a mass ratio of 2:1 between the two.

A method for preparing above-mentioned bast fibers for plastics reinforcement, comprises the following steps:

(1) Cut bast fibers to a length of 1˜20 mm to obtain chopped bast fibers; soak the chopped bast fibers in sodium hydroxide solution and agitate the mixture for 1˜20 mins, after rinse with water and drying, soak them in the aqueous solution of bast fiber treatment agent at a temperature of 80˜90° C. for 5 mins˜30 mins, then dry them until the solution is exhausted by the bast fibers and thus obtain surface-treated chopped bast fibers;

(2) Add in order the surface-treated chopped bast fibers, the coupling agent, the Functional Polyolefin wax and the antioxidant to a kneader preheated to 70˜80° C., agitate the mixture, and then obtain bast fibers for plastics reinforcement.

In step (1), the mass concentration of the sodium hydroxide solution is of 1%˜10%; the mass concentration of the bast fiber treating agent is of 10%˜50%; the rinse is of centrifugal type; the dry is meant to dry the fibers to the extent that the latter has a water content of 8%˜15% (normal water content of bast fibers).

In step (1), the drying is of the type of vacuum drying at a temperature of 90˜150° C. and to the extent that the fibers have a water content of less than 1%; the rinse is meant to rinse the fibers with water until the pH is between 7.0˜9.0.

In step (2), the agitation duration is 5˜10 mins; the agitation speed is 50˜300 rpm.

The principle of the invention is as follows: through washing away the impurities on fiber surface with dilute alkali, and then processing the fibers in aqueous solution of the treating agent, such as urea-formaldehyde resin prepolymer, trimethyl melamine resin or hexamethyl melamine resin, etc., where hydroxyl groups on the fiber surface react with hydroxymethyl groups of the treating agent, coating the fiber surface with a layer of urea-formaldehyde resin or melamine resin, thus the surface polarity of the bast fibers is reduced and the water absorption rate of the bast fibers also reduced, while the rigidity and heat resistance of the bast fibers increased; further, the coupling agent helps improve compatibility between bast fibers and plastics, and the Functional Polyolefin wax favors the amelioration of lubrication and dispersion inside the fibers.

Compared with the existing technology, Chopped bast fibers according to the invention present good color, rigidity and heat resistance, as well as excellent compatibility with plastics, and can be used in the preparation of high-performance short flax fiber\plastic composites, as reinforcement in the plastic matrix.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention is herein described in further detail in combination with, but shall not be limited to, the following preferred embodiments.

Example 1

(1) Cut 100 pts.wt. ramie fibers to a length of 1˜20 mm to obtain chopped ramie fibers; soak the chopped ramie fibers in sodium hydroxide solution (mass concentration 1%) and agitate the mixture for 20 mins, after rinsing with water to pH=7.0 and centrifugal drying, soak them in the aqueous solution (mass concentration 30%) of bast fiber treating agent (80 pts.wt. urea-formaldehyde resin prepolymer) at a temperature of 80° C. for 30mins until the solution is exhausted by the ramie fibers, then dry them in vacuum at a temperature of 110° C. to the extent that the fibers have a water content of less than 1% and thus obtain surface-treated chopped ramie fibers;

(2) Add in order the surface-treated chopped ramie fibers, 2 pts.wt. silane coupling agent, 9 pts.wt. Functional Polyolefin wax (mixture of 5 pts.wt. metallocene polyethylene wax and 4 pts.wt. maleic-anhydride-grafted metallocene polyolefin wax) and 0.4 pts.wt. antioxidant (antioxidant 1010 and antioxidant 168 with a mass ratio of 2:1) to a kneader preheated to 70° C., agitate the mixture for 5 mins at a speed of 100 rpm, and then obtain ramie fibers for plastics reinforcement; the ramie fibers for plastics reinforcement obtained herein take on a light yellow color, rigid and easily dispersed in resin without sticking or twisted together.

Example 2

(1) Cut 100 pts.wt. flax fibers to a length of 1˜20 mm to obtain chopped bast fibers; soak the chopped flax fibers in sodium hydroxide solution (mass concentration 10%) and agitate the mixture for 2 mins, after rinsing with water to pH=9.0 and centrifugal drying, soak them in the aqueous solution (mass concentration 20%) of bast fiber treating agent (90 pts.wt. trimethylol melamine resin) at a temperature of 90° C. for 30 mins until the solution is exhausted by the flax fibers, then dry them in vacuum at a temperature of 150° C. to the extent that the fibers have a water content of less than 1% and thus obtain surface-treated chopped flax fibers;

(2) Add in order the surface-treated chopped flax fibers, 8 pts.wt. coupling agent (4 pts.wt. titanium coupling agent and 4 pts.wt. rare-earth coupling agent), 4 pts.wt. Functional Polyolefin wax (mixture of 2 pts.wt. metallocene polypropylene wax and 2 pts.wt. metallocene polyethylene wax) and 0.5 pts.wt. antioxidant (antioxidant 1010 and antioxidant 168 with a mass ratio of 2:1) to a kneader preheated to 80° C., agitate the mixture for 10 mins at a speed of 50 rpm, and then obtain flax fibers for plastics reinforcement; the flax fibers for plastics reinforcement obtained herein take on a light yellow color, rigid and easily dispersed in resin without sticking or twisted together.

Example 3

(1) Cut 100 pts.wt. agave fibers to a length of 1˜20mm to obtain chopped agave fibers; soak the chopped agave fibers in sodium hydroxide solution (mass concentration 5%) and agitate the mixture for 5 mins, after rinsing with water to pH=8.0 and centrifugal drying, soak them in the aqueous solution (mass concentration 10%) of bast fiber treating agent (100 pts.wt. hexamethylol melamine resin) at a temperature of 85° C. for 20 mins until the solution is exhausted by the agave fibers, then dry them in vacuum at a temperature of 120° C. to the extent that the fibers have a water content of less than 1% and thus obtain surface-treated chopped agave fibers; (2) Add in order the surface-treated chopped agave fibers, 7 pts.wt. coupling agent (5 pts.wt. aluminum coupling agent and 2 pts.wt. isocyanate coupling agent), 7 pts.wt. Functional Polyolefin wax (mixture of 5 pts.wt. metallocene polyethylene wax and 2 pts.wt. oxidized metallocene polyolefin wax) and 0.4 pts.wt. antioxidant (antioxidant 1010 and antioxidant 168 with a mass ratio of 2:1) to a kneader preheated to 75° C., agitate the mixture for 5 mins at a speed of 300 rpm, and then obtain agave fibers for plastics reinforcement; the agave fibers for plastics reinforcement obtained herein take on a light yellow color, rigid and easily dispersed in resin without sticking or twisted together.

Example 4

(1) Cut 100 pts.wt. jute fibers to a length of 1˜20 mm to obtain chopped jute fibers; soak the chopped jute fibers in sodium hydroxide solution (mass concentration 3%) and agitate the mixture for 1 mins, after rinsing with water to pH=7.5 and centrifugal drying, soak them in the aqueous solution (mass concentration 30%) of bast fiber treating agent (50 pts.wt. urea-formaldehyde resin prepolymer) at a temperature of 88° C. for 25 mins until the solution is exhausted by the jute fibers, then dry them in vacuum at a temperature of 100° C. to the extent that the fibers have a water content of less than 1% and thus obtain surface-treated chopped jute fibers;

(2) Add in order the surface-treated chopped jute fibers, 8 pts.wt. coupling agent (5 pts.wt. isocyanate coupling agent and 3 pts.wt, rare-earth coupling agent), 1 pts.wt. oxidized metallocene polyolefin wax and 0.3 pts.wt. antioxidant (antioxidant 1010 and antioxidant 168 with a mass ratio of 2:1) to a kneader preheated to 78° C., agitate the mixture for 8 mins at a speed of 150 rpm, and then obtain jute fibers for plastics reinforcement; the jute fibers for plastics reinforcement obtained herein take on a light yellow color, rigid and easily dispersed in resin without sticking or twisted together.

Example 5

(1) Cut 100 pts.wt. agotai fibers to a length of 1˜20 mm to obtain chopped bast fibers; soak the chopped agotai fibers in sodium hydroxide solution (mass concentration 8%) and agitate the mixture for 15 mins, after rinsing with water to pH=8.5 and centrifugal drying, soak them in the aqueous solution (mass concentration 50%) of bast fiber treating agent (20 pts.wt. trimethylol melamine resin) at a temperature of 80° C. for 15 mins until the solution is exhausted by the agotai fibers, then dry them in vacuum at a temperature of 90° C. to the extent that the fibers have a water content of less than 1% and thus obtain surface-treated chopped agotai fibers;

(2) Add in order the surface-treated chopped agotai fibers, 0.1 pts.wt. isocyanate coupling agent, 5 pts.wt. Functional Polyolefin wax (mixture of 1 pts.wt. metallocene polyethylene wax, 2 pts.wt. metallocene polypropylene and 3 pts.wt maleic-anhydride-grafted metallocene polyolefin wax) and 0.1 pts.wt. antioxidant (antioxidant 1010 and antioxidant 168 with a mass ratio of 2:1) to a kneader preheated to 76° C., agitate the mixture for 8 mins at a speed of 250 rpm, and then obtain agotai fibers for plastics reinforcement; the agotai fibers for plastics reinforcement obtained herein take on a light yellow color, rigid and easily dispersed in resin without sticking or twisted together.

Example 6

(1) Cut 100 pts.wt. bast fibers (mixture of ramie and agotai fibers) to a length of 1˜20 mm to obtain chopped bast fibers; soak the chopped bast fibers in sodium hydroxide solution (mass concentration 6%) and agitate the mixture for 12 mins, after rinsing with water to pH=7.5 and centrifugal drying, soak them in the aqueous solution (mass concentration 30%) of bast fiber treating agent (50 pts.wt. hexamethylol melamine resin) at a temperature of 90° C. for 5 mins until the solution is exhausted by the bast fibers, then dry them in vacuum at a temperature of 150° C. to the extent that the fibers have a water content of less than 1% and thus obtain surface-treated chopped bast fibers;

(2) Add in order the surface-treated chopped bast fibers, 10 pts.wt. coupling agent (mixture of 2 pts.wt. silane coupling agent, 5 pts.wt. aluminum coupling agent and 3 pts.wt. rare-earth coupling agent), 10 pts.wt. Functional Polyolefin wax (mixture of 2 pts.wt. metallocene polyethylene wax, 3 pts.wt. metallocene polypropylene, and 3 pts.wt. oxidized metallocene polyolefin wax) and 0.5 pts.wt. antioxidant (antioxidant 1010 and antioxidant 168 with a mass ratio of 2:1) to a kneader preheated to 72° C., agitate the mixture for 7 mins at a speed of 280 rpm, and then obtain bast fibers for plastics reinforcement; the bast fibers for plastics reinforcement obtained herein take on a light yellow color, rigid and easily dispersed in resin without sticking or twisted together.

Even if the invention was described with reference to what is presently considered to be the most preferred embodiments, it must be understood that the invention shall not be limited to the above described embodiments, but that it is intended to include also different modifications, substitutions, combinations and simplifications which should be considered as equivalent technical solutions within the scope of the present invention. 

1. Bast fibers for plastics reinforcement, characterized in that: the bast fibers for plastics reinforcement consists of the following components by weight ratio: Chopped bast fibers 100 pts.wt. Bast fiber treating agent 0.1~100 pts.wt. Functional Polyolefin wax 1~10 pts.wt. Coupling agent 0.1~10 pts.wt. Antioxidants 0.1~0.5 pts.wt.


2. Bast fibers for plastics reinforcement according to claim 1, wherein the chopped bast fibers are chosen from at least one of the following fibers: ramie fiber, flax fiber, agave fiber, jute fiber and agotai fiber.
 3. Bast fibers for plastics reinforcement according to claim 1, wherein the bast fiber treating agent is urea-formaldehyde resin prepolymer, trimethylol melamine resin or hexamethylol melamine resin.
 4. Bast fibers for plastics reinforcement according to claim 1, wherein the Functional Polyolefin wax is chosen from at least one of the following components: metallocene polyethylene wax, metallocene polypropylene wax, oxidized metallocene polyolefin wax and maleic-anhydride-grafted metallocene polyolefin wax.
 5. Bast fibers for plastics reinforcement according to claim 1, wherein the coupling agent is chosen from at least one of the following components: silane coupling agent, titanium coupling agent, aluminum coupling agent, isocyanate coupling agent and rare-earth coupling agent.
 6. Bast fibers for plastics reinforcement according to claim 1, wherein the antioxidant is composed of antioxidant 1010 and antioxidant 168, with a mass ratio of 2:1 between the two.
 7. Method for preparing the bast fibers for plastics reinforcement according to claim 1, characterized in comprising the following steps: (1) Cut bast fibers to a length of 1˜20 mm to obtain chopped bast fibers; soak the chopped bast fibers in sodium hydroxide solution and agitate the mixture for 1˜20 mins, after rinse with water and drying, soak them in the aqueous solution of bast fiber treating agent at a temperature of 80˜90° C. for 5 mins˜30 mins, then dry them until the solution is exhausted by the bast fibers and thus obtain surface-treated chopped bast fibers; (2) Add in order the surface-treated chopped bast fibers, the coupling agent, the Functional Polyolefin wax and the antioxidant to a kneader preheated to 70˜80° C. , agitate the mixture, and then obtain bast fibers for plastics reinforcement.
 8. Method according to claim 7, wherein in step (1), the mass concentration of the sodium hydroxide solution is of 1%˜10%; the mass concentration of the bast fiber treating agent is of 10%˜50%; the rinse is of centrifugal type; the dry is meant to dry the fibers to the extent that the latter has a water content of 8%˜15%.
 9. Method according to claim 7, wherein in step (1), the drying is of the type of vacuum drying at a temperature of 90˜150° C. and to the extent that the fibers have a water content of less than 1%; the rinse is meant to rinse the fibers with water until the pH is between 7.0˜9.0.
 10. Method according to claim 7, wherein in step (2), the agitation duration is 5˜10 mins; the agitation speed is 50˜300 rpm. 